Diversity and survival:
It has been clear to many that a population of animals should benefit from variation within its bounds above and beyond the variation needed to elude the ill effects of inbreeding.  I am not a faithful fan of science fiction, but my friends who are assure me that the white armored troopers of the Star Wars series are all clones of an individual man.  That makes sense for a high risk occupation.  It should limit the grief a normal person would feel as one of a few survivors of a very large battle; they were all the same person in a manner of speaking, and the survival of many of the clones, including those uninvolved would not have been in question.  On the other hand everybody has a greatest weakness, be it emotional, social or biological.  Once the enemy or some virus finds the weakness, the whole population is in jeopardy.

This has been placed on a more firm evidential base.  (Vital Variation SCIENCE vol. 339. no. 6116 January 11, 2013 page 120 reviewing work by Gonzáles-Suárez and Revilla Ecol. Lett. 10.1111/ele.12036(2012)) Sure enough, after looking at what has happened to a lot of animals they concluded that along with low density and slow reproduction and maturation putting populations at greater risk of extinction when things get rough, variation in things like body size confer an advantage. 

So where does that put people?  Slow reproduction and slow growth and development are features humans have carried beyond any other life form.  So there is a strike against us.  Population density is a good thing by and large, but I think it’s pretty well established that humans have too great a population size planet wide.  We are in the midst of a great mass extinction of our own making.

The article says this is the sixth, and by standard criteria I’m sure it is.  But if you perch on the side of the Grand Canyon and view the far wall you cannot but be struck with the fact that the earth is in layers.  Each layer is about homogenous throughout its thickness but dramatically different from the layer above and below.  The cooling voice of sanity suggests that this reflects changes in the balance between deposition and removal at the ancient surface.  But abandoning sanity let me point out that this record so dramatically visible is about a billion years.  Pretty much it is the trilobite age.  If there were trilobites it was all under water the whole time.  So much for erosion.  If the layers are punctuated with times when currents scoured the sea bed then that scouring must have been going on almost all the time with only fits and starts of sedimentary buildup. 

The alternative must be that there were colossal changes in the sea bed that occurred quite abruptly with respect to the time spans of sedimentation.  And the fossils are different in every layer, of course.  So each line represents a really big extinction although not what is technically called a mass extinction.  Well that’s more than six, for sure. 

So really big extinctions are rather common compared with the few mass extinctions, one of which is visiting us now. 

As I said, our reproductive rate and long immaturity do not favor us.  Nor in fact does population density although usually it is a Good Thing. 

Our technology could be either our salvation or our destruction.  There is no telling before the event.

So what about our physical variation?  We score high on that one.  The “pigmy chimpanzee” is called a “bonobo” for one reason because they are not as small as real pygmies.  Humans vary quite a lot in size, stature and coloration.  So diversity is our friend and we have a lot.

Of course modern mating strategies are busily about reducing that diversity.  I should wonder that nobody has offered a cautionary note.  If you want to preserve your diversity you want people to marry kin.  That’s without even considering that it’s a biological necessity in the long run. 

Of course it doesn’t really make any difference.  It would take very many generations for diversity to be erased among humans.  If we pursue such strategies, we shall not have many generations, at least from the way I read the available data.

There have been 407 “distinct hosts served” this year whatever that means.

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